Steam sterilizers, also referred to as “autoclaves,” are widely used in a variety of applications for eliminating contaminating microorganisms from articles such as surgical instruments and other hospital equipment, laboratory equipment, and pharmaceutical and medical products.
In the operation of a steam sterilizer, after charging the sterilizer chamber with articles to be sterilized, air is drawn out of the chamber by applying a vacuum. Drawing of the vacuum is discontinued, and steam is then injected into the chamber. After the articles in the chamber have been exposed to steam for a sufficient time, drawing the vacuum can be resumed to remove steam, water vapor and condensate. In some cases, the cycle consisting of drawing the vacuum and injecting steam can be repeated while sterilizing a particular set of articles.
The vacuum is conventionally produced by using a pump to pump water through an ejector (also known as an “eductor”), a device comprising a narrowed passage, i.e., a venturi, for increasing the velocity of flow and thereby producing a vacuum. The water is typically circulated through the ejector through a path that includes a reservoir.
An ejector operates more efficiently at lower temperatures. For example, with a typical ejector, in order to reach a vacuum level of 700 mm of Mercury within five minutes, a water temperature of 29° C. is typically required. However, when an ejector is used to draw a vacuum on a steam sterilizer, steam, hot water vapor and hot condensate are introduced into the circulating water, increasing its temperature. Therefore, to maintain efficient operation of the ejector, cool water is added to the reservoir.
Because condensate and cooling water are added to the recirculating water stream, the total volume of water in the system continually increases, and it is necessary to discharge water to a drain. Plumbing codes typically require the effluent discharged by sterilizing equipment to a water drain to be at a temperature not greater than 140° F. (60° C.). Thus it is also necessary to add cooling water in order to bring the temperature of the effluent down to the required level. Large quantities of cooling water are required to achieve efficient ejector operation and to satisfy effluent temperature requirements. However, the significant water requirements of vacuum equipment associated with steam sterilizers have caused environmental concerns, especially in arid geographic areas.